1. Field of the Invention
The present invention relates to an apparatus and method for estimating Noise and Interference (NI) power in a communication system. More particularly, the present invention relates to an apparatus and method for estimating NI power using a periodic ranging code in a communication system.
2. Description of the Related Art
Research on a next-generation communication system is being conducted to provide Mobile Stations (MSs) with services capable of high-speed, high-capacity data transmission/reception. An example of the next-generation communication system is a communication system using the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (hereinafter referred to as an ‘IEEE 802.16 communication system’).
In the IEEE 802.16 communication system, a ranging operation is performed to adjust a time offset, a frequency offset and power between a Base Station (BS) and an MS. The ranging can be classified into initial ranging, periodic ranging, bandwidth request ranging and handover ranging according to their purpose.
Among others, the initial ranging operation and the periodic ranging operation are used in the IEEE 802.16 communication system, since it is possible to estimate Signal to Interference Noise Ratio (SINR) and Noise and Interference (NI) power used for power control of the IEEE 802.16 communication system through the initial ranging operation and the periodic ranging operation.
However, estimating NI power using the periodic ranging operation may cause an increase in error probability, and a description thereof will be given below.
First, the periodic ranging operation is performed in a state where there is no reference signal, for example, a pilot symbol. In this case, since the NI power is estimated in the state where there is no reference signal, the error probability may increase.
Second, an MS performs the periodic ranging operation using a periodic ranging code randomly selected from previously assigned periodic ranging codes. When the periodic ranging operation is carried out using a contention-based scheme in this way, the ranging codes transmitted from different MSs may collide with each other. The collision between ranging codes may eventually increase error probability for NI power estimation.
When the NI power estimation suffers an error, power control also undergoes error, and the power control error may cause a reduction in system performance of the IEEE 802.16e communication system.